Effects of NaCl and ethanol stresses on γ-aminobutyric acid synthesis in Kocuria kristinae

Abstract

Kocuria kristinae, one of the dominant strains in Kedong sufu, can generate γ-aminobutyric acid (GABA). NaCl and ethanol are added to sufu for preservation. This study aims to reveal the effects of NaCl and ethanol stresses on GABA synthesis in K. kristinae. The results suggested that high GABA production was obtained by adding 6% NaCl at the mid-exponential growth phase and 3% ethanol at the late exponential growth phase. Two GABA synthesis pathways were observed, including a new GABA synthesis pathway. Under NaCl stress, genes were upregulated by 1.46- to 3.67-fold in two synthesis pathways of GABA. Under ethanol stress, genes were upregulated by 1.20- to 6.39-fold in two synthesis pathways of GABA, except for speG and MAO. However, their corresponding metabolites were downregulated by 1.02- to 7.69-fold. The changes in genes and metabolites in the carbohydrate and amino acid metabolism pathways and in membrane transport suggested that different metabolic strategies were used to cope with NaCl and ethanol stresses in K. kristinae. The molecular mechanism in improving the production of GABA by NaCl and ethanol stresses was shown in K. kristinae. This study provides a theoretical basis for the development of GABA-enriched sufu by NaCl and ethanol stresses.